French Justice Minister Christiane Taubira has stepped down from her job, shortly before plans to strip people convicted of terrorism of their citizenship go before parliament.
Ms Taubira was known to disagree with the controversial proposals.
The citizenship plans were put forward after the 13 November Paris attacks in which 130 people were murdered.
"Sometimes staying on is resisting, sometimes resisting means leaving," she tweeted.
Ms Taubira, one of France's few senior black politicians, has been replaced by Jean-Jacques Urvoas who is seen as a supporter of the constitutional change and an ally of Prime Minister Manuel Valls.
Born in French Guiana, Ms Taubira, 63, has suffered racist taunts from the far-right during her time as justice minister.
Her left-wing leanings have put her increasingly at odds with official policy, especially after the November attacks - when the president announced a much tougher line on terrorism, BBC Paris correspondent Hugh Schofield reports.
State of emergency
A communique from the Elysee Palace said that President Francois Hollande had accepted the justice minister's decision to resign.
"They agreed on the need to bring her role to an end at a time when debate on constitutional revision begins in the National Assembly, today," the statement read.
Mr Valls was due to present the reforms before a committee at the National Assembly on Wednesday before they go before MPs next week. He told the BBC last week that France could not live forever under a state of emergency but as long as the threat remained all means had to be used "until we can defeat Daesh (so-called Islamic State).
The reforms include the right to declare a state of emergency under the constitution, which would make it easier for the French government to adopt strict powers such as police raids and house arrests.
The government aims to extend the three-month state of emergency imposed after the November attacks when it expires on 26 February.
President Hollande is going to miss Christiane Taubira because she performed a vital role in his government. Every time he took a move to the right, or was accused of doing so, he could point to his justice minister and say: "Don't worry, Christiane's still with me."
She was his left-wing shield, and he kept her in office to ward off attacks from inside the Socialists over his increasingly pro-business economic policies, and (since November) his tough new line on terror.
Taubira was the darling of the left. Pugnacious and outspoken, she saw through the gay marriage law, and promoted a liberal line on police and sentencing. By the same token, the right despised her and there is now much rejoicing in their ranks.
In the end, President Hollande could no longer pull off the act of political splits which allowed his government to include such mutually hostile forces as Manuel Valls (on the right) and Taubira (on the left).
The times being as they are, it was the left-winger who went.
In his communique, President Hollande praised Ms Taubira's part in pushing through same-sex marriage laws.
Last month the justice minister made plain her distaste of the plan to strip citizens with dual nationality of their French citizenship, arguing it " would not help the fight against terrorism in any way".
She said the plan was being dropped only for it be announced the following day by the prime minister with her appearing beside him.
Mr Valls described the reform as a "strong symbolic act against those who have excluded themselves from the national community".
There is a huge debate in France over whether the stripping of citizenship should apply only to dual nationals, our correspondent says.